1. Statement of the Technical Field
The present invention relates to the field of wireless communications and more particularly to a method and system for providing integration and a migration path between disparate wireless broadband systems in order to increase network capacity and performance.
2. Description of the Related Art
As the demand for high speed broadband networking over wireless communication links increases, so to does the demand placed on communication infrastructures. The result is that the capacities of even relatively new wireless communication technologies become quickly reached. Service providers have been deploying Evolution Data Only (“EV-DO”) based systems, such as 1xEV-DO systems (also referred to herein as “1x-DO”) to provide wireless broadband networking service to their customers. EV-DO systems are based on code division multiple access (“CDMA”) technology used to provide cellular telephony services such as are specified in the CDMA2000 specification. CDMA2000 is a family of 3G mobile telecommunications standards that use CDMA, a multiple access scheme for digital radio, to send voice, data, and signaling data (such as a dialed telephone number) between mobile stations (“MS”) and base stations.
In brief, CDMA communication allows many mobile stations and base stations to share the same frequency by encoding data with a pseudorandom noise code associated with an assigned channel. Typically, a system that operates within a 5 MHz frequency band can be divided into three 1.25 MHz carriers, into which the channels are allocated (the remaining 1.25 MHz of the frequency band is positioned between the carriers to allow for separation). CDMA systems that provide broadband data support may allocate one or more carriers to voice communications and the remainder to EV-DO communications.
Conceptual proposals have been made which propose the stacking of multiple EV-DO carriers to scale bandwidth. Carrier stacking is referred to as multi-carrier data only (“MC-DO”). However, these proposals fail to address integration with existing 1x-DO implementations or provide a migration path from these legacy installations to an MC-DO system. It is therefore desirable to have a method and system which provides a migration path from a 1x-DO system to an MC-DO system and which does not require customers to have to immediately replace 1x-DO MS hardware.
Whether 1x-DO or even MC-DO, EV-DO technology has limitations as compared with newer wireless broadband networking technologies such as broadband orthogonal frequency division multiplexing (“B-OFDM”). Like CDMA, OFDM is a technology that transmits multiple signals simultaneously over a single transmission path. Each signal travels within its own unique frequency range (sub-carrier), which is modulated by the data (text, voice, video, etc.).
OFDM uses a spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” that prevents the demodulators from seeing frequencies other than their own. Unlike EV-DO systems, OFDM systems do not require a guard band between sub-carriers. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. This is useful because in a typical terrestrial broadcasting scenario there are multi-path-channels in which the transmitted signal arrives at the receiver using various paths of different length. Because multiple versions of the signal interfere with each other, referred to as inter symbol interference, it becomes very hard to extract the original information. OFDM reduces the effect of this distortion. B-OFDM is the use of OFDM for broadband data transmission.
As compared with EV-DO, OFDM systems offer greater channel capacities and performance. However, EV-DO and OFDM systems are incompatible. This presents a very large problem for service providers due to the huge cost of deploying a wireless broadband infrastructure, not to mention the extreme cost associated with licensing portions of the frequency spectrum from the government. While service providers who have deployed an EV-DO system may recognize the benefits of newer technologies such as B-OFDM, they may not be in position to simply discard the EV-DO system and install an OFDM-based system. In addition, because customers' mobile stations are currently designed to support one system or the other, it presents a marketing challenge to get customers to simply replace EV-DO mobile stations they may have recently purchased with mobile stations that can run on a different technology. It is desirable to have a method and system which provides a migration path from an EV-DO system (whether 1x-DO or MC-DO) to B-OFDM without the need to purchase licenses for additional spectrum.
Multiple Input, Multiple Output Orthogonal Frequency Division Multiplexing (“MIMO-OFDM”) is an OFDM technology that uses multiple antennas to transmit and receive radio signals. MIMO-OFDM allows service providers to deploy wireless broadband systems that take advantage of the multi-path properties of environments using base station antennas that do not necessarily have line of sight communications with the MS.
MIMO systems use multiple antennas to simultaneously transmit data, in small pieces to the receiver, which processes the separate data transmissions and puts them back together. This process, called spatial multiplexing, can be used to proportionally boost the data-transmission speed by a factor equal to the number of transmitting antennas. In addition, since all data is transmitted both in the same frequency band and with separate spatial signatures, this technique utilizes spectrum very efficiently. It is therefore also desirable to have a method and system which provides a migration path from 1x-DO to MIMO-OFDM.